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In this study, the effect of Cl activation treatment on performance indicators of CdS/CdTe solar cells was investigated. We improved the performance of CdTe solar cells by applying a novel double treatment method that combines the CdCl2 dipping treatment and Freon (difluoro chloromethane) treatment methods that were previously studied. Conventional CdCl2 methanol dipping treatment (CdCl2 dipping treatment), Freon gas treatment that includes chlorine (Freon treatment), and CdCl2 dipping treatment + Freon treatment (double treatment) were performed, and the efficiencies, open circuit voltage (V OC ), and short circuit current (J SC ) for all three processes were observed. Although the efficiencies of the CdCl2 dipping treatment and Freon treatment were similar, there was a trade-off between the V OC and J SC in both processes. The double treatment sample shows an efficiency of 14.3%, which was higher than that of a single-treated sample. To investigate the characteristic change of each part of the solar cell, an equivalent circuit model in which the device was divided into a main junction and a back contact was used. In addition to electrical measurements, secondary ion mass spectroscopy (SIMS) and time of flight (TOF) analysis were performed. Through TOF measurement, drift mobility values for three treatment samples were calculated to be 1.1 cm 2/Vs, 1.8 cm 2/Vs, and 1.9 cm 2/Vs, respectively. With TOF measurement, it was proved that the double treatment had a significant influence on the efficiency of the sample.

Defects located at the $\text {E}\rm _{C}$ - 1.1 (eV) level, which are electro-optically active deep traps, generally have been overlooked since their presence cannot be detected except for those in highly resistive CdTe compounds. The origin of this trap is still debated on whether it is from Te vacancies or from dislocations induced by secondary phase defects in Te. We have grown high-resistivity Te-rich CZT ingots to clarify the origin of the 1.1 eV defects and to analyze the defect levels in the CZT samples by current deep level transient spectroscopy (I-DLTS)and photoluminescence (PL). From the analysis, defect levels such as shallow acceptor/donor, A-centers, Cd vacancies and Te antisite appeared to be in both high and low concentrations of Te inclusions, but the level of 1.1-eV defects exhibited dependence on the density of Te inclusion in the CZT samples. We also evaluated the effect of the 1.1-eV deep-level defects on the detector’s performance in point view of carrier trapping and de-trapping.

Semi-insulating Cd 0.9 Zn 0.1 Te:Pb crystals were grown by the vertical Bridgman method. Measurements of the current deep level transient spectroscopy (I-DLTS) revealed three trap levels in this material. Unlike other compensating dopants, CdZnTe:Pb samples do not show any Cd-vacancies defects and A-center levels. We subjected them to temperature-gradient annealing in Cd overpressure at 490–717 °C, and recorded an exponential relationship between the annihilation time of Te precipitates and the annealing temperature. The energy resolution of an annealed CdZnTe:Pb detector, tested using a 137 Cs radioactive source, gave an energy resolution of 2.5%.

High purity Pb-doped CdZnTe single crystals were grown by using the vertical Bridgman method. Their electrical properties and X-ray spectrum were investigated. The doping concentration of Pb was about 1 × 10 19 cm - 3 . The resistivity of Pb-doped CdZnTe single crystal was 2 × 10 9 Ω cm . The temperature dependence of the resistivity of these crystals was examined between the region of 200 and 300 K. The plot of log ( ρ ) versus 1000 / T was represented by a straight line with a slope of 380 meV. From the PL spectrum, we have confirmed that type conversion from p to n-type conductivity originated from the compensation process of Cd vacancies, which are the most abundant acceptors in CdZnTe. Also, the effects of Pb-doping on the mobility and X-ray spectra were studied by time-of-flight (TOF) and 241Am spectrum measurements.

The high-resistivity polycrystalline CdZnTe thick films are grown by thermal evaporation method. The electrical properties of polycrystalline CdZnTe having high resistivity were investigated using time of flight technique. We have measured the average drift mobility and mobility lifetime of polycrystalline CdZnTe. In the comparison of annealed samples at different conditions, the variation of resistivity in the polycrystalline CdZnTe is considered to be related to the fluctuation of carrier concentration. From the analysis of transient photocurrent of time of flight based on multiple trapping model, we have found that the two dominant localized states which is considered to be related to the Cd vacancy (E/sub V/+0.36 eV), and grain boundary defects (E/sub V/+0.75 eV) play a dominant role in increasing resistivity through compensation process.

Polycrystalline CdZnTe thick films were grown by thermal evaporation method using CdZnTe and CdZnTe:Cl source. Non-doped CdZnTe thick films have Te-rich stoichiometry having resistivity 3.3 × 109 Ωcm. The Cl-doped CdZnTe thick films have 1.2 × 1010 Ωcm in resistivity. To evaluate the role of Cl in the increasement of the resistivity, the density of localized states were calculated from the analysis of transient TOF (time of flight)current. From the comparison of Cl-doped CZT thick films with non-doped and O2 annealed CdZnTe thick films, we have found that Cl doping is related to the formation of states at EV + 0.75 eV region and oxygen reduces grain boundary related defects through formation TeO2 or CdTeO3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cd1−xZnxTe grown by high-pressure Bridgman method (HPB) has been known to be a good candidate for gamma-ray detection material. The metal contacting conditions are very important for the performance of gamma-ray detector. Therefore, it is essential to find proper contact technology. For these purposes, various contact methods (electroless deposition, thermal vacuum evaporation) and materials (Au, Pt) are attempted. From the measurement of current–voltage characteristics, gamma-ray spectroscopy and auger electron spectroscopy (AES), the physical properties of metal contact on the CdZnTe are analyzed and contact methods compared with one another. Electroless Pt deposition is found to have better properties than others in many respects.

A model of surface recombination velocity for n-type Hg 1− x Zn x Te is presented. It has been shown that, both experimentally and theoretically, the surface recombination velocity is dominated by Shockley–Read recombination mechanism at higher temperature and dominated by Auger process at low temperature. We have further developed a surface recombination theory for the narrow-gap semiconductor. It is concluded that the optimum conditions to reduce recombination velocity is about 2×10 11 cm −2 in the fixed charge density and the Cd 0.8 Zn 0.2 Te passivation layer thickness is between 140 and 160 nm.

Electro-migration of ionized/electrically active impurities in CdZnTe (CZT) was successfully demonstrated at elevated temperature with an electric field of 20 V/mm. Copper, which exists in positively charged states, electro-migrated at a speed of 15 μm/h in an electric field of 20 V/mm. A notable variation in impurity concentration along the growth direction with the segregation tendency of the impurities was observed in an electro-migrated CZT boule. Notably, both Ga and Fe, which exist in positively charged states, exhibited the opposite distribution to that of their segregation tendency in Cd(Zn)Te. A CZT detector fabricated from the middle portion of the electro-migrated CZT boule showed an improved mobility-lifetime product of 0.91 × 10−2 cm2/V, compared with that of 1.4 × 10−3 cm2/V, observed in an as-grown (non-electro-migrated) CZT detector. The optimum radiation detector material would have minimum concentration of deep traps required for compensation.

High purity Pb-doped CdZnTe single crystals were grown by the vertical Bridgman method and their electrical properties and X-ray sensitivity were investigated. The doping concentration of Pb was about 1 times 1019 cm-3. The resistivity of Pb-doped CdZnTe single crystal was 2 times 109 Omega-cm and its values were three orders higher than that of non-doped CdZnTe single crystals. The temperature dependence of resistivity of these crystals was performed between 200 K and 300 K region. The plot of log(rho) versus 1000/T was represented by straight lines and its slopes had shown the 380 meV. In addition to, the type of conductivity of this crystal was derived from the position of Fermi level and its shift in band gap to the temperature. From the PL spectrum, we have confirmed that these phenomena are originated from the compensation process of Cd vacancies which are the most abundant acceptor in CdZnTe. Also, the effects of Pb-doping on the mobility was studied by TOF (time of flight) measurement. X-ray sensitivity in the 241Am measurement was not exactly indicated due to the leakage current.

We measured the dependence of the energy gap in Bridgman-grown Cd1−xMnxTe crystals, 0≤x≤0.25, on the Mn mole fraction and temperatures from 40 to 300 K. We determined the Mn mole fraction and energy gap, respectively, from electron probe microanalysis and near-infrared Fourier-transform infrared transmission spectra. The energy gap increased linearly with an increase in the Mn content in the crystal and with a decrease in temperature. We formulated new equations from these experimental results, wherein we expressed the energy gap as a function of Mn mole fraction and temperature. Also, we compare our findings with published results.